Frequently, containers of volatile liquid are subject to internal pressure changes of such magnitude as to cuase the containers to burst from internal pressure or to collapse from internal vacuum unless they are reinforced to a degree which is prohibitive from the standpoint of cost and/or utilization, or unless they are vented. Thus, automobile gasoline tanks, for example, must be manufactured in a manner and from materials which are not prohibitively costly, or too heavy or cumbersome. Yet the gasoline which they contain is notoriously volatile and subject to vaporization, not only as a function of its temperature and surface area, but also as a result of the "sloshing" which takes place as the gasoline is agitated when the vehicle is in motion since, in effect, the gasoline and the atmosphere at its surface are being actively "churned" into each other, thus, by well-known physical principles, effectively increasing the surface area of the liquid gasoline which is available for evaporation to take place. In accordance with other well known physical principles relating to gases, changes in phase from liquid to gas will produce an increased volume if pressure is held constant; the alternative being to restrict volume increases causing the pressure to increase. Such pressure increases can be so substantial as to cause the tank to burst. Such pressure increases can also cause an associated fuel system of a vehicle to go out of control since the flow of fuel into the carburation system will be increased by the internal tank pressure independent of the regulation devices by which fuel flow normally is controlled.
In addition, when such pressures are not present, as the fuel is consumed from the tank, a vacuum is induced within the tank as a result of which, by operation of atmospheric pressure on the outside of the tank, makes it possible for the tank actually to collapse or, short of that, for fuel flow into an associated carburetion system to be reduced or even stopped since the vacuum can become of sufficient magnitude to overcome the fuel pump and/or the vacuum inducing capability of the carburetor.
Various means have been used to circumvent these problems, including incorporation of a vent tube or hole, usually in the top of the tank, or in the filler cap, whereby vapors under internal tank pressure may be relieved to the atmosphere, and tank vacuum may be relieved by air coming into the tank. Satisfactory as this may have been for the purpose of solving pressure differential problems, it has fallen into disfavor because of its environmental impact and wasting of energy, for as a practical matter the tank pressure and vacuum inducing causes are constantly changing, as a result of which the tank "breathes," alternately expelling gas vapor and sucking in air from the atmosphere. One adverse effect of this is to contaminate the atmosphere. Further, since those fractions of the gasoline most susceptable to evaporation are the lightest hydrocarbons, that is, components with the 4, 5 or 6 carbon atoms of the paraffinic, olefinic or aromatic series, and since there is now opinion in the technical community that these components are among those most susceptible to reaction with nitrogen dioxide in the presence of sunlight to produce the basis for the " photochemical smog" so well known, for example, in Southern California, the adverse effects of such emissions produce greater consequences than merely their presence in the atmosphere. With this in mind primarily, it has been proposed that all such gasoline tank vapor emissions must be fed into the carburetion system of the associated vehicle, but while this may help alleviate the environmental problem, it is not significantly effective with respect to mitigating the energy losses which also result from such tank "breathing."
According to well known physical principals, gasoline evaporates at its surface so long as the adjacent atmosphere remains unsaturated. Those constituents which so evaporate first and most readily are the ones having the lowest flash point, representing a valuable energy constituent of the gasoline. Thus, in a system where the atmosphere adjacent the surface of the gasoline is being maintained below the saturation level as by removal of vapors into the atmosphere or the associated carburetion system, there is a material and significant reduction in the energy potential of the gasoline as a fuel, due to removal therefrom by evaporation of low flash point constituents, and this is exagerated even more under conditions such as those which obtain in an automotive fuel system, where "sloshing" occurs and temperatures frequently become comparatively high.
Furthermore, in view of the highly competitive nature of such businesses as the automotive industry, an over-riding consideration of devices to circumvent these problems is that they must be structurally simple, operationally reliable, have low maintainence costs, and be cheap and easy to install and replace.
Accordingly, it is an object of the present invention to produce a device which will reduce or eliminate the venting from containers of volatile liquids or the introduction into such containers of atmospheric gases within desired pressure and vacuum limits.
It is another object of the present invention to provide a means for maintaining to the greatest degree practicable the saturation level of the atmosphere in a container for volatile liquids. Another object of the present invention is to provide a means for achieving the other objects of the present invention which is inexpensive to produce, structurally simple, and cheap and easy to install.